“As my grandmother got older, she begged my mother to give her grandchildren. She prayed to God for just one grandbaby before she died. You can imagine her excitement when she found out her prayers would be answered — twice over,” Castro said. “She was so excited that the day before Joaquín and I were born she entered a menudo cook-off, and she won $300! That's how she paid our hospital bill.”

Menudo immediately became a topic on Twitter.

Melissa Block (@NPRmelissablock), host of NPR's All Things Considered tweeted, “First mention of menudo at a convention? #DNC2012.”

Lizzie Skurnick (@lizzieskurnick) touted the accomplishment, “That's no joke, to win a menudo cook-off in San Antonio,” while author and former reporter at the L.A. Times @steveweinstein jokingly tweeted, “GOP rebuttal: Julián Castro's grandmother didn't build her menudo.”

The traditional Mexican soup is made with tripe, or beef stomach lining, as well as hominy, onions, peppers, spices and cilantro.

“Menudo, first of all, is a poor man's food. It was really the leftovers of the whole beef process,” La Gloria chef and restaurateur Johnny Hernandez said. “It's a huge tradition for Hispanics. We've grown up eating it.”

For his family, it has traditionally been something they enjoy on the weekends, usually with barbacoa. Many restaurants only serve the dish on weekends. It's also a staple at celebrations, such as New Year's, and it has been touted as a hangover cure.

Still, it's not a dish that most Americans are familiar with.

“There are cuts of meat that chefs have glorified over the years that have made their ways to fancy menus,” such as fajitas a generation ago, or beef cheeks and hearts, Hernandez said. “But menudo has never made that leap.”

That may change after Tuesday night.

To prepare menudo at home, the main element is time because the stomach lining has a tough texture, so it has to be cooked low and slow. There are two grades of tripe for menudo at the grocery store — standard and honeycomb, which is preferred because it uses the best cut of meat.

As for what exactly was in that famous Castro family recipe? That may remain a secret.

“I just never learned to cook any of the things I should have learned how to cook,” Rosie Castro said of her mother's recipe. “I remember that it had the traditional ingredients, which is the hominy, pigs feet and the tripe, and of course, the chili powder. But I don't know what combination or other spices.”

She has promised to see if another family member has the recipe. We'll share it if she does.